Quadrant shower tray

ronnyb_2

I am fitting an offset 900 X 760 quadrant shower tray. I've fitted the tray and tiled up to it. The actual cubicle is glass / aluminium rails with 2 sliding doors. The bottom aluminium rail or orbit as its described in the instructions sits on the tray in both corners but as the curve goes round towards the middle opposite the drain there is an increasing gap under the orbit to nearly 7mm. No amount of adjustment of the uprights solves this. Incidentally the shower tray is level on both it's straight edges. I suspect there is a slight dip in the curved part of the tray. I've emailed the manufacturers of the tray but received no reply. Any ideas or solutions would be welcome. Do I pack the gap with silicone or plumbers seal?